1. Field of the Invention
The invention relates to connectors for use with fiber optic cables.
2. Description of the Prior Art
The employment of fiber optic cables or light guides, also sometimes referred to as optical communication fibers, for the transmission of information-bearing light signals, is now an established art. Much development work has been devoted to the provision of practical low-loss glass protective outer coatings or jackets. The jacket makes them resemble ordinary metallic-core electrical cable upon superficial external inspection. Obviously, if fiber optic cables are to be used in practical signal transmission and processing systems, practical connectors for the connection and disconnection of fiber optic cables must be provided.
Before the prior art in respect to connectors, per se, is discussed, some references will be given for the benefit of the skilled reader in understanding the state of fiber optic art in general.
An article entitled "Fiber Optics" by Narinder S. Kapany, published in the SCIENTIFIC AMERICAN, Vol. 203, Pages 72-81, dated November, 1960, provides a useful background in respect to some theoretical and practical aspects of fiber optic transmission.
Of considerable relevance to the problem of developing practical fiber optic connectors, is the question of transfer efficiency at the connector. Various factors, including separation at the point of abutment, and lateral separation or offset, are among the factors effecting the light transfer efficiency at a connector. In this connection, attention is directed to the Bell System Technical Journal, Vol. 50, No. 10, December 1971, specifically to an article by D. L. Bisbee, entitled "Measurement of Loss Due to Offset, and End Separations of Optical Fibers." Another Bell System Technical Journal article of interest appeared in Vol. 52, No. 8, October 1973 and was entitled "Effect of Misalignments on Coupling Efficiency on Single-Mode Optical Fiber Butt Joints" by J. S. Cook, W. L. Mammel and R. J. Grow.
The patent literature also contains much information relative to the state of this art. For example, U.S. Pat. No. 3,624,816 describes a "Flexible Fiber Optic Conduit." The device described there uses a plurality of light conducting fibers in a flexible cable type arrangement.
Concerning the utility of fiber optic cables and therefore the utility of connectors for such cables, various systems are described in the patent literature which employ fiber optic cables. One example of such a utilization system is described in U.S. Pat. No. 3,809,908.
Yet another patent of interest is entitled "Glass Fiber Optical Devices," U.S. Pat. No. 3,589,793. That reference relates to the fiber optic bundles and the glass fibers themselves, as well as to a method of fabrication for the fiber optic elements themselves.
A selection of U.S. patents relation more particularly to optical cable connectors includes U.S. Pat. Nos. 3,790,791; 3,734,594; 3,637,284; 3,572,891; 3,806,225; 3,758,189 and 3,508,807 are representative of the connector prior art.
It is known that, in a fiber optic bundle, it is very desirable to compress the fibers as close together as possible, so that the unused, or void area between fibers, is reduced to a minimum. It is also known that one important factor in joined fiber optic cable connections having the least light-loss at transfer from surface to surface is provision of an axially tight contact at the fiber end interfaces. This is true whether or not an interface gel or other material is used at the fiber bundle abutment.
In the prior art, there has been mainly reliance on close tolerances or interface materials to deal with the problems present. These problems include optical gaps at abutment points, mechanical damage to the bundle end surfaces and the potential for variations in optical transmission through an insufficiently positive abutment. The maintenance of close tolerances involves high costs and other disadvantages and optical gaps and mechanical damage to the fiber bundle ends can deteriorate the light transfer. Vibration effects have deleterious effects including possible introduction of modulation on the light intensity level.
The manner in which the present invention deals with such problems of the prior art will be understood as this description proceeds.